Bifidobacterium bacteria are reported to exhibit various physiological effects such as inhibitory effects against harmful intestinal bacteria, intestinal function controlling effects and immunoactivating effects. A number of products containing Bifidobacterium bacteria have been put on the market, for example, in the form of fermented milk products or live-bacteria-containing preparations, and they have established a firm position in the market. In particular, a strong preference to fermented milk food and drink enables continuous intake of Bifidobacterium bacteria and they are therefore a suitable form for administration.
Bifidobacterium bacteria exhibit most of their physiological effects by producing acetic acid or the like as a metabolite after reaching the intestines. In order to produce satisfactory effects, they must reach the intestines in the viable form. The extent to which bacteria reach the intestines has conventionally been judged with their recovery rate from feces as an index. Described specifically, the number of living bacteria in the feces reflects the extent to which the bacteria reach the intestines so that the extent has been confirmed by collecting the feces of the human beings to which the bacteria were administered and counting the number of living bacteria (collection rate) in the feces.
It is generally considered that Bifidobacterium bacteria have difficulty in reaching the intestinal tracts because of weak tolerance to an acid and bile. In other words, when they are taken orally, there is a possibility of them being killed by gastric juice or bile prior to reaching the intestines.
In recent years, improvement of various production techniques enables an increase in the very number of bacteria which can be administered so that even if some of the bacteria are killed, physiological effects can still be expected from the remaining ones. Upon production of fermented foods containing Bifidobacterium bacteria, a variety of components for improving bacterial viability during storage, for example, N-acetyl glucosamine, pantothenic acid, peptides and lactulose are added. Their action is considered to heighten the extent to which Bifidobacterium bacteria reach the intestines after their administration.
In order to attain stronger physiological effects, a greater number of viable bacteria must be caused to reach the intestines. There is accordingly a demand for improving the extent to which the bacteria reaching the intestines. An administration test to human beings becomes inevitable for finding the extent, that is, a recovery ratio of them from feces. Cumbersome and long-term works necessary for the test have however hampered the implementation of such a test.
There are some reports on the production of a strain endowed in advance with tolerance to gastric juice or bile which will otherwise be a barrier against the orally taken bacteria. For example, it is described in Japanese Patent Laid-Open No. Hei 9-322762 that use of Bifidobacterium bacteria exhibiting high tolerance to acids, bile salt and oxygen enables culture on skim milk or the like under aerobic conditions without adding a growth promoting substance. In International Journal of Food Microbiology, 47, 25-32(1999), described are two strains of Bifidobacterium bacteria having high tolerance to an acid and bile.
Considering the possibility of improving the extent to which bacteria reach the intestines upon their administration by the use of such highly tolerant bacteria, the present inventors created such a strain having high tolerance to an acid and bile, prepared a syrup-containing fermented milk food or drink by using the strain, administered it to human beings and found a recover ratio from feces. As a result, it has been revealed that there is not always a correlation between the tolerance and the recovery ratio.
Accordingly, an object of the present invention is to construct a convenient and accurate assessing system which reflects the extent to which Bifidobacterium bacteria in a fermented milk food or drink reach the intestines. Another object of the present invention is to create a strain superior in the extent to the conventional Bifidobacterium bacteria and provide a Bifidobacterium-bacteria-containing fermented milk food or drink by using the bacteria.